Building codes require that public spaces have electrically operated emergency lighting and signage (collectively “emergency loads” or “safety units” hereafter) in case of a power outage so that the occupants of the building can evacuate safely. Such emergency loads of course require an auxiliary power source that functions during a power outage.
Common building construction uses wallboard or other types of panels mounted on studs for the walls, or on joists for ceilings to define individual occupancy spaces (rooms, halls, etc.). The spaces between the studs or joists behind the panels are usually void or occupied by insulation. Particularly in commercial buildings and multiple dwellings, some ceilings use panels that fit into metal frames suspended from I-beams or poured concrete layers. For the sake of simplicity, all of these various types of room-defining panels having voids behind them will hereafter be referred to as “walls”.
Many types of buildings have their emergency loads mounted in visible locations of halls, stairways, and other evacuation routes. These loads must be completely visible when deployed during power outages. But mounting these emergency loads so as to be visible when power is available may not be desirable for a couple of reasons. The emergency loads are often eyesores. And emergency loads mounted in visible locations are vulnerable to vandalism and to damage during cleaning, painting, etc.
These concerns have been known for a long time. Solutions have been difficult to devise.